^99mTc/¹⁸⁸Re-labelled lipid nanocapsules as promising radiotracers for imaging and therapy: formulation and biodistribution

Purpose: This study focusses on a promising carrier system for imaging and therapeutic purposes using lipid nanocapsules. To assess their potential for clinical use, we labelled nanocapsules with Tc-99m and Re-188 and analysed some kinetic biodistribution parameters after intravenous injection in rats. Methods: Lipophilic complexes [Tc-99m/Re-188(S3CPh)(2) (S2CPh)] (Tc-99m/Re-188-SSS) were encapsulated within the nanoparticles during their manufacture with quantitative yield and satisfactory radiochemical purity. Rats were injected intravenously with 3.7 MBq Tc-99m/Re-188-labelled nanocapsules and sacrificed at 5, 15 and 30 min and 1, 2, 4, 8, 12, 16, 20 and 24 h. Results: Dynamic scintigraphic acquisitions showed predominant hepatic uptake, and ex vivo counting indicated a long circulation time of labelled nanocapsules, with a half-life of 21 +/- 1 min for Tc-99m and 22 +/- 2 min for Re-188. Very weak urinary elimination was observed, indicating good stability of Tc-99m and Re-188 labelling. Conclusion: Tc-99m/Re-188-SSS nanocapsules can be obtained with high yield and satisfactory radiochemical purity. The biodistributions of Tc-99m/Re-188-labelled nanocapsules are close to those of classical PEG-coated particles and show good stability of Re-188/Tc-99m-SSS labelling.